Riffing off Loki's comment, there is also the consideration that there may not have been time to both think of and implement that idea. Quoting the script, which doesn't have timestamps but from what I remember this all happens pretty quickly:
(the Enterprise has just arrived at Earth)
PICARD: This is Captain Picard of the Enterprise. I am taking command
of the fleet. Target all of your weapons onto the following
coordinates. ...Fire on my command.
DATA: Sir, the coordinates you have indicated do not appear to be a
PICARD: Trust me Data.
RIKER: The fleet's responded, sir. They're standing by.
(the fleet attacks and a circular aperture opens in the Borg ship and
a Borg sphere launches before the ship explodes)
Given that 'the fleet' is firing, it's probably OK to say the Enterprise is at a reasonable distance from the sphere:
PICARD: Mister Hawk. Pursuit course. ...Engage.
Confirming our guess. You don't have to pursue something if you're already close enough to... do whatever you want to do. Tractor beams have a relatively short range, from what I remember.
[snip a few lines of continuous dialogue, no great time passes]
DATA: Sensors show chronometric particles emanating from the sphere.
PICARD: They're creating a temporal vortex.
RIKER: Time travel!
(the Enterprise suffers a shockwave)
PICARD: Data, report!
DATA: We appear to be caught in a temporal wake.
WORF: Captain, ...Earth.
[at this point Earth is put on screen, everyone looks up and gasps, because it looks like it's completely metalled over]
DATA: The atmosphere contains high concentrations of methane, carbon
monoxide and fluorine.
PICARD: Life signs?
DATA: Population ...approximately nine billion. ...All Borg!
So less than a minute after we started pursuing them, already they have changed history. What use a tractor beam now?